1. Field of the Invention
The present invention relates to a fuel reforming apparatus for a polymer electrolyte membrane fuel cell.
2. Description of the Related Art
FIG. 20 shows as an example the construction of a conventional fuel reforming apparatus for a polymer electrolyte membrane fuel cell. As shown in the drawing, the conventional fuel reforming apparatus comprises a reformer A, a carbon monoxide converter B and a carbon monoxide selective oxidation reactor C.
Steam 6, which is obtained as follows, is supplied into the reformer A. Specifically, water 5 within a gas-liquid separator 26 is introduced into an evaporator (steam generator) 13, and a water-steam mixture 4 obtained by partially evaporating the water is introduced into the gas-liquid separator 26 so as to separate the mixture 4 into water 7 and steam 6.
The steam 6 thus obtained is mixed with a reforming fuel 8 consisting of, for example, a natural gas in the reformer A, and the resultant mixture is introduced into a reforming catalyst layer 14 included in the reformer A. While the fuel 8 passes through the reforming catalyst layer 14, a so-called xe2x80x9creforming reactionxe2x80x9d to form hydrogen (H2), carbon monoxide (CO) and carbon dioxide (CO2) is carried out while the fuel 8 and the steam 6 pass through the reforming catalyst layer 14. Since the reforming reaction is an endothermic reaction, hydrogen remaining in the fuel (exhaust gas) of the fuel cell stack (not shown) is burned in a burner 10 attached to the reformer A so as to generate heat within a burner space chamber 9. The heat thus generated is transmitted to the reforming catalyst layer 14 within the reformer A so as to bring about the reforming reaction.
A center plug 11 for forming a radiation heat transmitting section 91 utilizing burner gas of a high temperature and a convection heat transmitting section 92 utilizing burner gas of a high and intermediate temperature is arranged within the burner space chamber 9.
It should be noted that, in the fuel reforming apparatus of the polymer electrolyte membrane fuel cell, it is necessary to remove carbon monoxide formed by the reforming reaction because carbon monoxide markedly impairs the performance of the fuel cell stack even if carbon monoxide is contained in a very small amount. Such being the situation, the carbon monoxide converter B comprising a carbon monoxide converting catalyst layer 27 and a cooling device 28 buried in the carbon monoxide converting catalyst layer 27 and formed of a heat transmitting tube wound in, for example, a spiral form is arranged downstream of the reformer A in the conventional fuel reforming apparatus of the polymer electrolyte membrane fuel cell.
A reaction is carried out between carbon monoxide and steam within the carbon monoxide converting catalyst layer 27 so as to form hydrogen and carbon dioxide. Since this reaction is an exothermic reaction, the cooling device 28 is buried in the catalyst layer 27 so as to remove the heat generated by the exothermic reaction.
It should also be noted that the fuel gas coming from the reforming catalyst layer 14 has a high temperature and, thus, the fuel gas noted above is not adapted for the transforming reaction of carbon monoxide. Such being the situation, a cooling device 16 for cooling the inlet gas of the carbon monoxide converter (cooling device arranged upstream of the carbon monoxide converting catalyst layer) is arranged upstream of the carbon monoxide converting catalyst layer 27. Also, in order to further remove carbon monoxide, which was left unreacted in the carbon monoxide converting catalyst layer 27, the carbon monoxide selective oxidation reactor C consisting of a carbon monoxide selective oxidation catalyst layer 29 and a cooling device 30 buried in the carbon monoxide selective oxidation catalyst layer 29 are arranged downstream of the carbon monoxide converter B.
The air 2 is mixed with the reformed gas before entering the carbon monoxide selective oxidation catalyst layer 29 and, thus, oxygen contained in the air selectively carries out the reaction with carbon monoxide within the carbon monoxide selective oxidation catalyst layer 29 so as to form carbon dioxide, with the result that the carbon monoxide concentration is lowered to 10 ppm or less. In this case, hydrogen also reacts with oxygen so as to form steam. However, it is possible to suppress the reaction of hydrogen by the function of the catalyst if the air amount and the temperature of the catalyst layer are adjusted at appropriate values.
The carbon monoxide selective oxidation reaction is an exothermic reaction and, thus, the cooling device 30 is buried in the catalyst layer 29 in order to remove the heat generated by the exothermic reaction and to maintain the temperature at an appropriate value. Also, the gas passing through the carbon monoxide converting catalyst layer 27 is not adapted for the carbon monoxide selective oxidation reaction if the gas noted above is allowed to flow directly into the carbon monoxide selective oxidation catalyst layer 29. Therefore, the cooling device 20 is mounted on the inlet port of the catalyst layer 29 for the carbon monoxide selective oxidation reaction so as to lower the temperature of the gas passing through the carbon monoxide converting catalyst layer 27 and, then, the gas with the lowered temperature is supplied into the catalyst layer 29 for the carbon monoxide selective oxidation.
As a method for combining and integrating the particular system for providing a single apparatus, a stacked type structure is proposed in, for example, a first prior art, i.e., Japanese Patent Disclosure No. 7-126001, and a second prior art, i.e., Japanese Patent Disclosure No. 7-133101. Each of these prior arts is directed to the case where, for example, methanol is used as raw fuel material. It is taught that the apparatuses such as a burner, a reformer, carbon monoxide converter, and a carbon monoxide selective oxidation reactor are successively stacked one upon the other so as to make it possible to utilize effectively the heat recovery in an evaporator, the endothermic reaction in the reformer, the exothermic reaction in each of the carbon monoxide converter and the carbon monoxide selective oxidation reactor in the case where the operating temperature in every apparatus is low and the temperature differences between the apparatuses is small such that the operating temperature of each of the reformer and the carbon monoxide converter is 200 to 300xc2x0 C., the operating temperature of the carbon monoxide selective oxidation reactor is 150xc2x0 C. and the operating temperature of the evaporator is 100 to 150xc2x0 C. As a result, it is made possible to provide a reforming apparatus performing the function of steam-reforming, for example, methanol.
The body portion of the polymer electrolyte membrane fuel cell, in which electricity is generated by the reaction between hydrogen and oxygen carried out under a low temperature in the presence of a catalyst, can be made compact, compared with the body portion of another fuel cell, e.g., a phosphoric acid type fuel cell. In addition, since the operating temperature is low, the body portion of the polymer electrolyte membrane fuel cell is expected to be applied to, for example, a domestic power generating apparatus and an automatic vending machine.
However, in the conventional fuel reforming apparatus of the polymer electrolyte membrane fuel cell, the reactors included in the apparatus differ from each other in the required temperature level, as described above. Therefore, it was necessary to arrange individually the reformer, the cooling device at the inlet port of the carbon monoxide converter, the cooling device at the inlet port of the carbon monoxide selective oxidation reactor, and the carbon monoxide selective oxidation reactor and, then, to connect these apparatuses using pipes. Such being the situation, it was unavoidable for the fuel reforming apparatus to be rendered bulky.
It should also be noted that the carbon monoxide selective oxidation reactor is a reactor inherent in the fuel reforming apparatus of the fuel cell that is operated under a low temperature. Since it is necessary to use both the carbon monoxide selective oxidation reactor and the cooling device thereof, it was difficult to miniaturize the fuel reforming apparatus of the solid high molecular weight fuel cell.
Under the circumstances, to miniaturize the fuel reforming apparatus is one of the serious problems which must be solved for putting the polymer electrolyte membrane fuel cell to practical use. It should also be noted that the efficiency of the polymer electrolyte membrane fuel cell system must be prevented from being lowered by the improvement to miniaturize the system so as to require a larger amount of the fuel for obtaining the same amount of the power generation.
The combined integral type reforming apparatus for the fuel cell of the stacked type structure disclosed in prior art 1 and prior 2 referred to previously is formed on the assumption that a liquid fuel such as methanol is used as the raw fuel material. Therefore, the operating temperatures of the constituting apparatus are low and the difference in temperature between the constituting apparatus is small such that the operating temperature of each of the reformer and the carbon monoxide reactor is 200 to 300xc2x0 C., the operating temperature of the carbon monoxide selective oxidation reactor is 150xc2x0 C., and the operating temperature of the evaporator is 100 to 150xc2x0 C. Such being the situation, the function as a reforming apparatus can be performed even if the system is made compact by employing the stacked type structure.
On the other hand, in the case where the raw fuel materials such as methane and propane are subjected to steam reforming, the operating temperature of the reformer is high and, in addition, the difference in temperature among the constituting apparatus is large such that the operating temperature of the reformer is 700 to 750xc2x0 C., the operating temperature of the carbon monoxide converter is 200 to 300xc2x0 C., and the carbon monoxide selective oxidation reactor is 150xc2x0 C. Under the circumstances, if methane or propane is applied to the stacked type structure disclosed in, for example, prior art 1 and prior art 2, the amount of the heat migration from the reformer into the carbon monoxide converter or the carbon monoxide selective oxidation reactor tends to be rendered large so as to make it difficult to maintain the carbon monoxide converter and the carbon monoxide selective oxidation reactor at suitable temperatures.
In the stacked type structure, it is necessary to arrange a heat insulating layer or a cooling means between the reformer and the carbon monoxide converter or the carbon monoxide selective oxidation reactor in order to suppress the migration of heat. In the former case, i.e., arrangement of a heat insulating layer, the object of making the system compact is impaired. The object of making the system compact is also impaired in the latter case. In addition, system efficiency is impaired.
In the reforming apparatus disclosed in the prior arts referred to previously, the side surface of each of the reactors is brought into contact with the outer air atmosphere and, thus, a heat insulating layer is required for suppressing the heat dissipation. However, in order to suppress the heat dissipation from the reforming reactor that is operated at 700 to 750xc2x0 C. to a level equal to that of another reactor, a heat insulating layer several times as much as the heat insulating layer for the other reactor is required so as to impair the object of making the apparatus compact. In addition, since the dissipated heat is not recovered, it is difficult to improve the thermal efficiency. Since the heat dissipation is increased with increase in the temperature of the reactor, the reduction of the thermal efficiency tends to be rendered prominent in, particularly, the case where methane or propane is used as the raw fuel material and, thus, the reforming reaction is carried out at a high temperature. It follows that required is a technology in which hydrogen and methane contained in the exhaust gas of the fuel cell is burned in the reformer having the highest operating temperature by using a burner so as to supply heat such that water is evaporated by the residual heat amount of the burner exhaust gas, and in which, cooling devices that permits setting the operating temperatures of the reformer, the carbon monoxide converter and the carbon monoxide selective oxidation reactor in the order mentioned are arranged for processing the gas on the process side of the reforming apparatus such that heat is effectively recovered by the cooling device and the heat dissipated from the reactor is also recovered so as to improve the efficiency of the system and permit making the system compact.
The present invention, which has been achieved to overcome the problems described above, is intended to provide a compact fuel reforming apparatus for a polymer electrolyte membrane fuel cell, which does not invite an increase in the required fuel consumption regardless of the raw fuel material.
According to a first aspect of the present invention, which is intended to achieve the object described above, there is provided a fuel reforming apparatus for a polymer electrolyte membrane fuel cell, comprising a reformer, a carbon monoxide converter, a carbon monoxide selective oxidation reactor, a cooling device for cooling the inlet gas of the carbon monoxide converter, and a cooling device for cooling the inlet gas of the carbon monoxide selective oxidation reactor,
characterized in that each of the reformer, the carbon monoxide converter, the carbon monoxide selective oxidation reactor, the cooling device for cooling the inlet gas of the carbon monoxide converter, and the cooling device for cooling the inlet gas of the carbon monoxide selective oxidation reactor is formed cylindrical; the reformer is arranged in the center of the installing plane, the carbon monoxide converter is arranged on the installing plane in the outer circumferential portion of the reformer, and the carbon monoxide selective oxidation reactor is arranged on the installing plane in the outer circumferential portion of the carbon monoxide converter so as to make these apparatuses integral; the cooling device for cooling the inlet gas of the carbon monoxide converter is arranged on inlet side of the carbon monoxide converter; and the cooling device for cooling the inlet gas of the carbon monoxide selective oxidation reactor is arranged on the inlet side of the carbon monoxide selective oxidation reactor.
According to the first aspect of the present invention, the constituting devices of the fuel reforming apparatus are arranged such that the device having a high temperature level is arranged in the center, and the other devices are arranged around the device having a high temperature level so as to permit the temperature level to be gradually lowered from the center toward the outer region of the fuel reforming apparatus. As a result, the temperature gradient between the adjacent devices is diminished so as to minimize the heat migration between the adjacent devices. It follows that it is possible to combine and make integral the constituting devices so as to render the resultant fuel reforming apparatus compact even if the constituting devices arranged independently or separated from each other by a heat insulating material for preventing the heat dissipation are not connected to each other by pipes. In addition, it is possible to maintain the operating temperature of each reactor at an appropriate level. What should also be noted is that the heat transmitted from the reactor having a high inner temperature to the outside is utilized for maintaining the temperature of the reactor on the outside so as to improve the thermal efficiency.
According to a second aspect of the present invention, which is intended to achieve the object described above, there is provided a fuel reforming apparatus for a polymer electrolyte membrane fuel cell, comprising a reformer, a carbon monoxide converter, a carbon monoxide selective oxidation reactor, a cooling device for cooling the inlet gas of the carbon monoxide converter, and a cooling device for cooling the inlet gas of the carbon monoxide selective oxidation reactor,
characterized in that each of the reformer, the carbon monoxide converter, the carbon monoxide selective oxidation reactor, the cooling device for cooling the inlet gas of the carbon monoxide converter, and the cooling device for cooling the inlet gas of the carbon monoxide selective oxidation reactor is formed in the shape of a parallelepiped; the reformer, the carbon monoxide converter, the carbon monoxide selective oxidation reactor are arranged in the order mentioned and mounted on an installing plane; these reactors are combined and made integral; the cooling device for cooling the inlet gas of the carbon monoxide converter is arranged on the inlet side of the carbon monoxide converter; and the cooling device for cooling the inlet gas of the carbon monoxide selective oxidation reactor is arranged on the inlet side of the carbon monoxide selective oxidation reactor.
According to the second aspect of the present invention, the temperature gradient between the adjacent constituting devices of the fuel reforming apparatus is diminished so as to suppress the heat migration between the adjacent constituting devices. It follows that it is possible to combine and make integral the constituting devices of the fuel reforming apparatus so as to render the fuel reforming apparatus compact, even if the constituting devices separated from each other with a heat insulating material are not connected to each other by using pipes.
According to a third aspect of the present invention, which is intended to achieve the object described above, there is provided a fuel reforming apparatus for a polymer electrolyte membrane fuel cell, comprising a reformer, a carbon monoxide converter, a carbon monoxide selective oxidation reactor, a cooling device for cooling the inlet gas of the carbon monoxide converter, and a cooling device for cooling the inlet gas of the carbon monoxide selective oxidation reactor,
characterized in that of the reformer is formed cylindrical; each of the carbon monoxide converter, the carbon monoxide selective oxidation reactor, the cooling device for cooling the inlet gas of the carbon monoxide converter, and the cooling device for cooling the inlet gas of the carbon monoxide selective oxidation reactor is formed in the shape of a parallelepiped; the reformer, the carbon monoxide converter and the carbon monoxide selective oxidation reactor are arranged in the order mentioned and mounted on an installing plane such that the carbon monoxide converter and the carbon monoxide selective oxidation reactor are combined with the reformer so as to form an integral structure, the integral structure being for cooling the installing plane; the cooling device for cooling the inlet gas of the carbon monoxide converter is arranged on the inlet side of the carbon monoxide converter; and the cooling device for cooling the inlet gas of the carbon monoxide selective oxidation reactor is arranged on the inlet side of the carbon monoxide selective oxidation reactor.
According to the third aspect of the present invention, it is possible to thermally separate the reformer having a high temperature level from the other reactors having a relatively low temperature. Also, since the reformer is shaped cylindrical, it is possible to transmit effectively the heat generated from the burner arranged within the reformer to the reforming catalyst layer. Further, since the carbon monoxide converter, the carbon monoxide selective oxidation reactor, the cooling device for cooling the inlet gas of the carbon monoxide converter, and the cooling device for cooling the inlet gas of the carbon monoxide selective oxidation reactor are shaped parallelepiped and combined to form an integral structure, it is possible to make compact the fuel reforming apparatus of the polymer electrolyte membrane fuel cell.
According to a fourth aspect of the present invention, which is intended to achieve the object given previously, there is provided a fuel reforming apparatus for a polymer electrolyte membrane fuel cell according to any one of the first to third aspects, characterized in that a steam generator for obtaining a reforming steam, which is supplied to the reformer, is combined with the reformer so as to form an integral structure.
According to the fourth aspect of the present invention, the steam generator is also combined with the reformer so as to make the fuel reforming apparatus more compact.
According to a fifth aspect of the present invention, which is intended to achieve the object given previously, there is provided a fuel reforming apparatus for a polymer electrolyte membrane fuel cell according to any one of the first to fourth aspects, characterized in that the steam generator is arranged within a combustion space container included in the reformer so as to be positioned in the vicinity of the outlet port of the burner exhaust gas.
According to the fifth aspect of the present invention, it is possible to make the steam generator integral with each of the reactors without obstructing the heat transmission of the burner gas and the catalyst layer in the reformer. As a result, it is possible to make the fuel reforming apparatus compact without inviting an increase in the consumption of the fuel.
According to a sixth aspect of the present invention, which is intended to achieve the object stated previously, there is provided a fuel reforming apparatus for a polymer electrolyte membrane fuel cell according to any one of the first to third aspects, characterized in that a carbon monoxide converting catalyst layer constituting a part of the construction of the carbon monoxide converter is arranged in a divided fashion, and a cooling device is arranged intermediate between the divided parts of the carbon monoxide converting catalyst layer.
According to a seventh aspect of the present invention, which is intended to achieve the object stated previously, there is provided a fuel reforming apparatus for a polymer electrolyte membrane fuel cell according to any one of the first to third aspects, characterized in that a catalyst layer for the carbon monoxide selective oxidation reaction, the catalyst layer constituting a part of the construction of the carbon monoxide selective oxidation reactor, is arranged in a divided fashion, and a cooling device is arranged intermediate between the divided parts of the catalyst layer for the carbon monoxide selective oxidation reaction.
According to the seventh aspect of the present invention, it is possible to render the temperature distribution uniform within the catalyst layer for the carbon monoxide selective oxidation reaction and to make the fuel reforming apparatus compact.
According to an eighth aspect of the present invention, which is intended to achieve the object given previously, there is provided a fuel reforming apparatus for a polymer electrolyte membrane fuel cell according to any one of the first to third aspects, characterized in that a cooling device is arranged downstream of a catalyst layer for the carbon monoxide selective oxidation reaction, the catalyst layer constituting a part of the construction of the carbon monoxide selective oxidation reactor, so as to be combined with the fuel reforming apparatus in a manner to form an integral structure.
According to the eighth aspect of the present invention, the portion that is locally heated to a high temperature within the catalyst layer is decreased, compared with the prior art in which the cooling is performed by burying a heat transmitting pipe within the catalyst layer. As a result, it is possible to decrease the amount of the catalyst to the minimum level required and to make the entire apparatus compact.
According to a ninth aspect of the present invention, which is intended to achieve the object given previously, there is provided a fuel reforming apparatus for a polymer electrolyte membrane fuel cell according to the first aspect, characterized in that an annular header provided with at least eight fine holes, which are arranged equidistantly, for supplying the air to a catalyst layer for the carbon monoxide selective oxidation, the catalyst layer constituting a part of the construction of the carbon monoxide selective oxidation reactor, is arranged outside the carbon monoxide selective oxidation reactor.
According to the ninth aspect of the present invention, it is possible to supply the air uniformly to the carbon monoxide selective oxidation reactor, even if the reformer, the carbon monoxide converter, the carbon monoxide selective oxidation reactor, the cooling device for cooling the inlet gas of the carbon monoxide converter, and the cooling device for cooling the inlet gas of the carbon monoxide selective oxidation reactor are formed cylindrical and combined to form an integral structure. It follows that it is possible to make the fuel reforming apparatus compact.
According to a tenth aspect of the present invention, which is intended to achieve the object given previously, there is provided a fuel reforming apparatus for a polymer electrolyte membrane fuel cell according to the first aspect or the second aspect, characterized in that a clearance for the heat insulation is formed between the partition wall of the reformer and the partition wall of the carbon monoxide converter.
According to the tenth aspect of the present invention, even if the reformer, the carbon monoxide converter, the carbon monoxide selective oxidation reactor, the cooling device for cooling the inlet gas of the carbon monoxide converter, and the cooling device for cooling the inlet gas of the carbon monoxide selective oxidation reactor are formed cylindrical and combined to form an integral structure such that the reformer having a high temperature level and the carbon monoxide converter having a low temperature level are positioned adjacent to each other, it is possible to suppress the migration of heat between the two. Further, it is possible to absorb the difference in elongation between the reformer having a high temperature level and the carbon monoxide converter having a low temperature level, the difference in elongation being caused by the thermal expansion. As a result, it is possible to suppress the thermal stress so as to overcome the problem in terms of the construction and the mechanical strength. It follows that it is possible to miniaturize the fuel reforming apparatus.
According to an eleventh aspect of the present invention, which is intended to achieve the object stated previously, there is provided a fuel reforming apparatus for a polymer electrolyte membrane fuel cell according to any one of the first to third aspects, characterized in that the cooling medium of the cooling device for cooling the inlet gas of the carbon monoxide converter is provided by a mixture consisting of steam before entering the reformer and the fuel.
According to the eleventh aspect of the present invention, the reforming gas can be cooled and, at the same time, a mixture of steam and fuel is heated before the mixture is introduced into the reformer. As a result, it is possible to achieve heat recovery. It follows that it is possible to make the fuel reforming system compact without lowering the power generating efficiency of the fuel cell system.
According to a twelfth aspect of the present invention, which is intended to achieve the object stated previously, there is provided a fuel reforming apparatus for a polymer electrolyte membrane fuel cell according to the sixth aspect, characterized in that the carbon monoxide converter is divided into at least two parts, and the cooling medium of the cooling device arranged between the divided parts of the carbon monoxide converter is provided by the steam generated from a steam generator or a mixture of water and steam.
According to the twelfth aspect of the present invention, the heat recovery can be achieved by heating a mixture of water and steam so as to make it possible to render the fuel reforming system compact without lowering the power generating efficiency of the fuel cell system.
According to a thirteenth aspect of the present invention, which is intended to achieve the object given previously, there is provided a fuel reforming apparatus for a polymer electrolyte membrane fuel cell according to the seventh aspect, characterized in that the carbon monoxide selective oxidation reactor is divided into at least two parts, and the cooling medium of each of the inlet cooling device, the intermediate cooling device and the outlet cooling device of the divided carbon monoxide selective oxidation reactor is provided by a part of the cooling water for the fuel cell stack.
According to the thirteenth aspect of the present invention, it is unnecessary to newly prepare a cooling medium, and the heat recovery can be achieved. It follows that it is possible to render the fuel reforming apparatus compact without lowering the power generating efficiency of the entire fuel cell system.